1. Field of the Invention
The invention generally relates to methods for forming semiconductor devices and more particularly relates to methods for processing a semiconductor substrate surface.
2. Description of the Related Art
In the field of integrated circuit and flat panel display fabrication, multiple deposition and etching processes are performed in sequence on the substrate within one or more processing chambers to form various design structures. Processes such as etching, physical vapor deposition (PVD), chemical vapor deposition (CVD), chamber cleaning and conditioning, etc. are well known in the industry and each process requires appropriate ways to detect the completion of the desired reaction inside a substrate processing chamber and cleaning of residue build-up on the substrate or the wall of the substrate processing chamber.
In general, silicon oxide, silicon nitride, metal oxide, or metal containing materials are deposited on the surface of a substrate as well as on all exposed surfaces in the substrate processing chamber. These materials may need to be etched or selectively removed in a subsequent process. In addition, these materials or residues may accumulate inside in the substrate processing chamber and must be removed from the chamber surfaces prior to the next deposition or etching process. Otherwise, the material may flake off and deposit on a substrate, thereby compromising the integrity of features formed thereon.
For example, an etch process can be used to remove materials from substrate surface. Plasma etch involves reacting a silicon-containing material on the surface of the substrate with a plasma to generate reaction intermediates as etchants and etch the silicon-containing material on the substrate surface. A requirement in such processes is a prompt termination of etching immediately after the first through, or clear, opening has been developed in the substrate. Stopping the etching process by a predetermined time is not practical because of the differences in film thickness on the surface of a wafer substrate and small surface area of active devices on a small portion of the substrate.
However, conventional end point detectors for plasma etch do not operate reliably during deep trench processes and when device surface areas are small. Such detectors focus a laser on the material to be etched and monitor the phase of the light reflected from the material. As the material is etched (removed), the phase of the reflected light changes in proportion with the depth of the etched area. In this manner, the detector monitors the etch depth and can cause the etching process to stop upon achieving a predetermined depth. To measure minute phase changes, the equipment must be accurately calibrated, and such equipment requires repeated recalibration. Also, as line widths become narrower, maintaining the laser focus upon a bottom of a trench is becoming difficult.
The second class of the end point detectors includes optical emission spectrometry (OES) detectors. These detectors comprise a data acquisition system and a plasma optical emission receiver and detect a change in intensity of one or several wavelengths of the plasma optical emission related to an etched or underlying layer. Sensitivity of these detectors diminishes with either complexity of spectrums or intensity of the plasma as the spectral lines of interest become obscured by background spectrum. Therefore, reliable and accurate end point detection which is critical during plasma etch remains an elusive goal.
On the other hand, pre-cleaning and removal of residual materials from substrate surface or chamber walls may use various chemical compounds that are ignited by exposure to plasma and react with the residual materials to form volatile compounds which can be exhausted from the chamber. Alternatively or additionally, such chemical compounds may form etching species which bombard chamber surfaces to dislodge residue from chamber components. During the time when the chamber cleaning operation is performed, the production of semiconductor devices cannot continue. As a result, the effective productivity of the chamber, as measured by substrate throughput, decreases significantly. To increase the chamber productivity, it is necessary to quickly finish the cleaning operation and restart the production promptly after the end of the cleaning operation. Therefore, it is imperative to precisely determine the end point of a cleaning process.
One method of detecting the end point of the cleaning process monitors a variation in a prescribed light wavelength emitted by the plasma. However, it is difficult to correctly detect the end point of the cleaning operation using this method because light emitted from lamps used to heat the substrate also heats, reacts with or otherwise affects the wavelength monitor, distorting the wavelength reading and resulting in over-cleaning or under-cleaning.
Another method of detecting the endpoint of a cleaning process is to observe the conditions within the chamber through a quartz view port. During processing within the chamber, residue accumulates on the view port, thereby blocking the view into the chamber. As the cleaning process progresses, the residual material is removed from the view port and all the other surfaces in the chamber as well, until the view port is clean and line of sight into the chamber is restored. Once line of sight into the chamber has been restored, the process is continued for approximately 20 to 30 seconds to ensure that the cleaning process is complete. The line of sight detection method does not provide an accurate determination of the endpoint and requires the use of cleaning time beyond the point in time when a clean view port is detected to assure adequate cleaning of the chamber.
In the area of integrated circuit fabrication, time spent in processing substrates and cleaning chambers is an important issue which manufacturers monitor. Time spent cleaning the chamber can be a factor limiting production capabilities. Accordingly, there is a need for a method which is accurate and consistent in determining the endpoint of a process performed inside a chamber. Preferably, the end point of a substrate removal or cleaning process can be determined by adapting existing hardware, monitors, and analyzers in a new process.
Therefore, there is a need for a novel end point detection method to be used for substrate processing or cleaning inside a substrate processing system. There is also a need for real time monitoring of substrate processing reactions or chamber cleaning efficiency.